1. Technical Field
The present invention relates in general to storage systems, and in particular disk drives. Still more particularly, the present invention relates to a write head having a recessed overcoat to improve performance.
2. Description of the Related Art
A hard disk drive (HDD) is a digital data storage device that writes and reads data via magnetization changes of a magnetic storage disk along concentric tracks. As application programs and operating systems become longer with more lines of program code, and data files, particularly graphics files, become larger, the need for additional storage capacity on the HDD increases. Since the trend in HDD design is towards the use of smaller, rather than larger, disks, the solution to increasing the storage capacity of magnetic storage disks is to increase the areal density of data stored on the disk.
Currently, there are two main types of magnetic storage on a magnetic disk: longitudinal and perpendicular. FIGS. 1a and b depict these two types of storage. FIG. 1a depicts the older technology of longitudinal recording. Longitudinal recorded bits 100 are stored when a longitudinal write head 102 magnetizes areas of a magnetic disk 104 in an orientation that is longitudinal to a track 118 on the magnetic disk 104. As shown, the magnetic moment of each subsequent recorded bit is opposing, such that each north pole faces a south pole and vice versa. These opposing moments result in a repulsive force, which leads to long-term instability of the magnetized areas, thus leading to eventual lost data. Nonetheless, longitudinal recording has traditionally been the accepted method of storage because of the materials used to fabricate magnetic disk 104 and the technological limitations on how small a pole tip of longitudinal write head 102 can be and still produce enough flux field to write data.
Modern disk fabrication materials have paved the way for perpendicular recording. These disk fabrication materials typically use a cobalt-chromium ferromagnetic thin film on an amorphous ferromagnetic thin film. This combination of materials affords both ultra-high recording performance along with high thermal stability. The concept of perpendicular recording is illustrated in FIG. 1b. Perpendicular-recorded bits 106 are stored on a perpendicular recording medium 108 as anti-parallel magnets in relation to one another in an orientation that is normal (perpendicular) to the surface of the perpendicular recording medium 108. Because the perpendicular-recorded bits 106 obey the pull of magnetic poles, they do not have the repulsive force of longitudinal recordings, and thus the perpendicular-recorded bits 106 are more stable.
While materials used to construct perpendicular recording medium 108 address part of the technological challenge of perpendicular recording, the other challenge is to fabricate a perpendicular write head 110 having a write pole tip 112 whose tip area is small enough to record the perpendicular-recorded bit 106 without overlapping an area reserved for another perpendicular-recorded bit 106. This overlap must be avoided not only for bit areas on a same track 120, but on bit areas on other tracks (not shown) as well. Thus, the aspect ratio (AR) of linear density (bits per inch—BPI) to track density (Tracks Per Inch—TPI) should be controlled at 1:1 (BPI:TPI) or at most 2:1 to avoid Adjacent Track Interference (ATI).
Furthermore, the perpendicular write head 110 must be able to produce a magnetic field that is powerful enough to magnetize an area for a perpendicular-recorded bit 106 without overwriting other bit areas or having to be so close to the surface of perpendicular recording medium 108 as to make head crashes likely. Furthermore, as write pole tip 112 is scaled to tighter dimensions and constrained by the AR requirements described above, the amount of write field coming out at the tip of write pole tip 112 is attenuated and may be insufficient to magnetize the bit fields.
With reference now to FIGS. 2a–c, there are depicted details of a typical read/write head 200. FIG. 2a is a vertical cross-section view, not to scale, FIG. 2b is an Air Bearing Surface (ABS) view (as shown from the perspective described in FIG. 2a as “View 2B”), not to scale, and FIG. 2c (as shown from the perspective described in FIG. 2a as “View 2C”) is a top cross-section view, not to scale, of read/write head 200. (As is known to those skilled in the art of hard disk drives, as a disk spins under a read/write head, the small space between the read/write head and the disk is maintained by pressure of air passing between the read/write head and the disk surface, creating an “Air Bearing Surface,” or ABS.)
The write head element 110, as seen in FIG. 1b, of head 200 is formed over an insulation layer 204 deposited on a second ferromagnetic shield layer (S2) 206 of a read head element 208. A first write pole piece (P1) layer 210 is plated over insulation layer 204. A Pole Tip Pedestal (PTP) 212 is formed on P1 layer 210 at the ABS. A bottom Back Gap (BG) element 214 is formed over P1 layer 210 at the end distal to the ABS.
An edge 217 of PTP 212 defines a Zero Throat Height (ZTH). An inset insulation layer 218 is formed on P1 layer 210 in the region between the PTP 212 and the BG element 214. After a Chemical and Mechanical Polishing (CMP) planarization step, write gap layer 216 is deposited over the PTP 212 and inset insulation layer 218. A second pole tip (P2) 203 is formed on write gap layer 216 at the ABS, and an upper element 220 of BG element 214 is also formed. A yoke extends from the write pole tip 112 to the edge of the BG element 214 nearest to the ABS.
The Track Width (TW) is defined by the width of P2 203. A coil 222 is formed over write gap layer 216 in the region between P2 203 and upper element 220 of BG element 214. Coil 222 is typically coplanar with the P2 203. Alternatively, coil 222 may be above and/or below P2 203. A coil insulation layer 224 is formed between the coils in coil 222. After a second CMP planarization, a hard-baked resist layer 226 is formed over coils 222 and coil insulation layer 224.
A pole (P3) structure 114 is connected to the tip of P2 203 and the upper element 220 of BG element 214. The tip of P2 203 has a portion which lies under the P3 114 to stitch the two layers. The P3 114 structure is recessed away from the ABS.
First and second leads 228 and 230 connect a Magneto-Resistive (MR) sensor 231, which is sandwiched between first and second gap layers 248 and 250, to a read/write circuit, such as a read/write circuit 416 shown in FIG. 4. Gap 250 overlays a first MR shield S1 252.
First and second leads 228 and 230 are connected to first and second conductors 232 and 234, respectively, at conductive vias 236 and 238. The conductors are in turn connected by conductive vias 240 and 242 to leads (not shown) which extend to the read/write circuit. The write coil 222 is connected to write coil pads 244 and 246, which are connected to leads (not shown) that extend to the read/write circuit.
A limitation of the head 200 shown in FIGS. 2a–c is the exposed nature of P3 114. This exposure not only presents unwanted opportunity for P3 114 to be damaged, but is also encourages stray flux fields to emanate outside of the focus required to write to perpendicular-recorded bit 106 seen in FIG. 1b. 
What is needed, therefore, is a perpendicular write head that has a very small write pole tip that is able to generate sufficient flux fields for magnetizing data bits areas without ATI issues, and a method to manufacture such a write head.